This invention relates generally to an apparatus and a method for conserving fuel during dynamic braking of locomotives (i.e., for operating the locomotives so that less fuel is used than would be used by heretofore conventional controlled dynamic braking). The invention relates more particularly, but not by way of limitation, to such apparatus and method utilizing a respective dynamic braking proportioning unit on each diesel locomotive of a train consist.
In the railroad industry attention has been given to ways of conserving fuel during the operation of trains because, for example, of the money that can be saved when fuel is saved. This attention to fuel conservation has been directed, at least in part, to ways of operating in more fuel efficient manners the locomotive propulsion or driving mechanisms which drive electrical traction motors to which the locomotive wheels are connected. That is, this focus has been on controlling the operation of the engines, such as through throttle setting control. Examples of this focus are disclosed in U.S. Pat. No. 4,344,364 to Nickles et al. and the references cited therein.
Another focus of this attention to fuel conservation would be on how to obtain fuel conservation from control of the locomotive stopping or braking mechanisms. Many conventional diesel locomotives are equipped with dynamic braking systems. A principle behind these dynamic braking systems is the utilization of the electrical traction motors as electrical generators to generate electrical power in response to the mechanical rotation imparted by the turning locomotive wheels connected to the traction motors, which generated power is dissipated within a large resistance grid located within the locomotive so that the dissipation causes a retarding force to act against the turning locomotive wheels.
These dynamic braking systems are designed to consume a substantial amount of power, such as up to 3000 horsepower. This creates a great deal of heat within the resistance grid. To maintain the resistance grid of a locomotive at an acceptable temperature level, cooling fans mounted on the locomotive are used. These fans are operated by the diesel engine(s) of the locomotive; therefore, fuel must be consumed during dynamic braking to power and the engine(s) to drive the fans. A typical fuel consumption rate per locomotive is 25 gallons per hour during dynamic braking as compared to a fuel consumption rate of 5 gallons per hour during locomotive idling. This difference in fuel consumption is especially significant because a typical train consist has more than one locomotive so that the consumption differential is multiplied by the number of locomotives in dynamic braking, which is the total number of locomotives for any level of conventional dynamic braking.
In such a typical train consist wherein more than one diesel locomotive is used to provide propulsion and braking for the train consist, the locomotives are mechanically and electrically coupled together. The electrical connection includes a trainline comprising several electrical conductors along which control signals are sent from the controlling locomotive at the command of the engineer. With respect to dynamic braking, it is controlled through a lever at the engineer's control stand. When the engineer moves this lever into a dynamic braking position, two of the wires within the electrical trainline are energized. In conventional dynamic braking operation, the signals along these two wires are provided in common to all of the coupled locomotives to obtain similar dynamic braking from each locomotive. Thus, all of the locomotives operate at the higher dynamic braking, fuel consumption rate regardless of how much braking is needed.
As is known to the art, one of the wires energized during dynamic braking is designated "B" and is referred to as the brake setup line. The other wire is given the letter designation "BC" and is referred to as the brake control line. When the dynamic braking lever is moved into its initial position, the B wire is immediately energized to the 74VDC level, which is the maximum voltage used on the conventional trainline known to the art. When a locomotive receives this signal, all the engines of the locomotive respond to increasing from idle speed to braking speed for driving the cooling fans (as knwon to the art, the engines are first disconnected from the alternators which drive the traction motors). The BC wire is a proportional signal, derived from the amount of movement of the engineer's dynamic braking control lever; it ranges from 0VDC (no braking) to 74VDC (full dynamic braking) for a conventional trainline.
To illustrate the effect of conventional dynamic braking, a train consist powered by four diesel locomotives is used as an example. It is assumed that each locomotive is capable of consuming 3,000 horsepower during dynamic braking, and that each locomotive consumes 5 gallons per hour when its engines are idling and 25 gallons per hour when they are driving the cooling fans during dynamic braking. Under these assumptions and the foregoing type of operation, a total of 100 gallons per hour would be consumed by the four locomotives under all dynamic braking conditions once the B wire has been energized to indicate dynamic braking (i.e., B=74VDC). This consumption rate is irrespective of what the BC signal is. This is shown in the following table:
TABLE I ______________________________________ Individual Braking Horsepower Consumption by Locomotive Lever Volts Number GPH Position B BC 1 2 3 4 Total ______________________________________ Idle 0 0 0 0 0 0 20 0% 74 0 0 0 0 0 100 25% 74 18.5 750 750 750 750 100 50% 74 37.0 1500 1500 1500 1500 100 75% 74 55.5 2250 2250 2250 2250 100 100% 74 74.0 3000 3000 3000 3000 100 ______________________________________
In view of the foregoing, there is the need for a more efficient way of operating the locomotives during dynamic braking so that the maximum fuel consumption is not used at all levels of dynamic braking.